1. Field of the Invention
The present invention relates to an optical disk playback apparatus and a decoder.
2. Description of the Related Art
Optical disk playback systems to playback optical disks compliant with a CD standard perform various displays based on information played back from the optical disk. For example, generally in CD standards, based on Q channel data (hereinafter, called “sub-Q data”) of sub-code information recorded in a lead-in area, track numbers and time information assigned to the track numbers, and the like are recorded in the lead-in area, as the sub-Q data of the sub-code information. Hence, the optical disk playback system reads out the sub-Q data from the lead-in area and decodes/playbacks the data, and thereby various displays can be performed.
Furthermore, a CD-TEXT standard has been proposed for recording TEXT information such as album titles and song titles in addition to audio information on an optical disk. Note that in the CD-TEXT standard, the TEXT information has a maximum of 8 blocks for each language, and one block has a maximum of 255 packs. One pack as a minimum unit consists of 18 bytes, 2 bytes of which are a CRC (Cyclic Redundancy Check) code. In the CD-TEXT standard, the TEXT information in the above format is recorded as R-W channel data (hereinafter, called “sub-R-W data”) of the sub-code information in the lead-in area. Hence, optical disk playback apparatuses compliant with the CD-TEXT standard (hereinafter, called “CD-TEXT playback apparatuses”) can display the TEXT information by reading out the sub-R-W data from the lead-in area and decoding/playing back the data.
FIG. 18 shows the configuration of a conventional CD-TEXT playback apparatus. See for example Japanese Patent Application Laid-open Publication No. 2003-36650.
An optical pickup 301 reads out information recorded on an optical disk 100 by irradiating laser light onto the optical disk 100 and detecting return light. A preamp 302 generates an RF signal by amplifying with a predetermined gain a light-detected signal from the optical pickup 301. Further, the preamp 302 binarizes the RF signal, an analog signal, to convert into a binary digital signal. An EFM demodulator 303 performs EFM (Eight to Fourteen Modulation) demodulation on the binarized RF signal generated in the preamp 302. The EFM-demodulated signal is sent to a sub-code decoder 304.
The sub-code decoder 304 decodes the sub-code information. Of the decoded sub-code information, sub-P and sub-Q data is sent to a microcomputer 306, and sub-R-W data is sent to a CD-TEXT decoder 305. Note that the sub-code decoder 304 performs CRC based on a CRC code included in the sub-Q data and detects whether the result of decoding the sub-Q data is normal. The CRC result is sent to the microcomputer 306 before the sub-Q data is sent.
The CD-TEXT decoder 305 (a “decoder”) decodes into the TEXT information according to the CD-TEXT standard from the sub-R-W data sent from the sub-code decoder 304. Also, each time TEXT information is decoded into, the CD-TEXT decoder 305 performs CRC based on a CRC code included in the TEXT information to detect whether the result of decoding into the TEXT information is normal. One bit indicating this CRC result (e.g., “1” when normal and “0” when not normal) is sent to the microcomputer 306.
The microcomputer 306 controls the whole of the optical disk playback system, that is, the CD-TEXT playback apparatus overall. For example, when the CRC result for the sub-Q data sent from the sub-code decoder 304 is normal, the microcomputer. 306 acquires the sub-Q data from the sub-code decoder 304 and stores it in a RAM 307. Also, when the CRC result of one bit sent from the CD-TEXT decoder 305 indicates being normal, the microcomputer 306 acquires 16 bytes of TEXT data (ID1 to ID4 of one byte each and 12 bytes of TEXT content) that is the result of decoding into the TEXT information from the CD-TEXT decoder 305 and stores it in the RAM 307.
Then, the microcomputer 306 analyzes TOC (Table of Contents) information based on the sub-Q data stored in RAM 307 to acquire information about positions on the optical disk 100 where desired music programs are recorded. While playing back a desired music program based on the position information, synchronously, the microcomputer 306 reads out the TEXT data stored in the RAM 307 and displays the TEXT information.
Note that in order to utilize the existing mechanisms of conventional CD-TEXT playback apparatuses, a microcomputer having a data bus width of 4 or 8 bits or the like is often used as the microcomputer 306, although high-performance microcomputers of a 32/64-bit data bus width have been developed in recent years. As such, because a low-performance microcomputer 306 is used, it is difficult to perform in parallel the processing of the sub-Q data (10 bytes) sent from the sub-code decoder 304 in 1/75 sec (13.3 ms) corresponding to one sub-coding frame, and the real-time processing of the TEXT data (64 bytes) sent from the CD-TEXT decoder 305 in each 1/75 sec.
Accordingly, the conventional CD-TEXT playback apparatus compliant with the CD-TEXT standard first accesses the lead-in area and reads out the sub-code information, and the sub-code decoder 304 decodes the sub-Q data and performs CRC. Then, if the CRC result for the sub-Q data is normal, the apparatus accesses the lead-in area again and reads out the sub-code information, and the CD-TEXT decoder 305 decodes the sub-R-W data into the TEXT information and performs CRC.
Moreover, the microcomputer 306 acquires the TEXT data and the CRC results from the CD-TEXT decoder 305, and determines, if respective CRC results for packs of the TEXT information are consecutively normal, that the TEXT information is present, and if CRC results are not consecutively normal, that no TEXT information is present.
The conventional CD-TEXT playback apparatus as shown in FIG. 18 has to wait for the completion of the decoding of the sub-Q data and CRC and the re-access to the lead-in area in order to determine whether or not TEXT information is recorded on an optical disk. Also for optical disks compliant with CD standards other than CD-TEXT, before determining that no TEXT information is present on the optical disk, the decoding of the sub-Q data and CRC and the re-access to the lead-in area and then the decoding of the TEXT information and CRC have to be completed. This causes the delay of the determination of whether TEXT information is present itself and the delay of optical disk playback processing to be performed after the determination of whether TEXT information is present, such as the display of TEXT information and producing audio output.
In the conventional CD-TEXT playback apparatus as shown in FIG. 18, by the time the microcomputer acquires 16 bytes of TEXT data from the CD-TEXT decoder 305, the microcomputer has to perform a procedure: acquiring one bit of CRC result, and determining the CRC result. This causes an increase in the processing load on the microcomputer, and also the delay of optical disk playback processing such as the display of TEXT information decoded-into in the CD-TEXT decoder and producing audio output.